Certain work vehicles are equipped with a so-called Hydro Static Transmission (HST). In an HST work vehicle, a hydraulic pump is driven by an engine, and a traveling motion hydraulic motor is driven by hydraulic fluid discharged from the hydraulic pump. Traveling motion of the work vehicle is thereby brought about. In an HST work vehicle of this type, the vehicle speed and traction force can be controlled through control of the engine speed, the pump displacement of the hydraulic pump, the motor displacement of the traveling motion hydraulic motor, and the like (see Japan Patent Laid-open Patent Publication JP-A-2004-144254).
In a work vehicle such as the aforedescribed, it is desirable to be able to lower the vehicle speed only, without lowering the engine speed. The reason is that, in a case in which, for example, a work implement is to be driven immediately after lowering the vehicle speed, when the engine speed has been lowered, it will take more time to increase the driving force of the work implement. For this reason, certain work vehicles are equipped with an inching pedal. The operator operates the inching pedal in order to reduce the vehicle speed. When the inching pedal is operated, depending on the quantity of depression of the inching pedal, the pilot pressure to the pump displacement control cylinder that controls the tilting angle of the hydraulic pump is reduced. In so doing, the pump displacement is reduced. As a result, the vehicle speed can be lowered without lowering the engine speed.